In order to mass production of semiconductor packages such as BGA (Ball Grid Array) packages, mold array process (MAP) has been widely implemented. During molding processes of MAP, a plurality of substrate units formed within a molding area of a substrate strip are continuously encapsulated by an encapsulant. Mold array process related technologies have been revealed in R.O.C. Taiwan patent number 1240395 and patent publication number 200818349 which further indicate that chips on substrate units are the major factors affecting the mold flow speeds but fail to disclose the impacts of side rails of molding area located outside the substrate units during MAP.
FIG. 1 shows conventional mold flows on a substrate strip to form an encapsulant during conventional MAP. A substrate strip 110 includes a plurality of substrate units 111 arranged in an array in each molding area 112. Usually, there are one or more molding areas 112 formed on the substrate strip 110 to define the encapsulated areas of the substrate strip 110. At least a chip 120 is disposed on each substrate unit 111 and is electrically connected to the corresponding substrate unit 111 by a plurality of bonding wires 140 or by other electrical connecting components. Several encapsulants 130 are formed on the corresponding molding areas 112 to continuously encapsulate the chips 120 in an array on the substrate units 111.
It was well known that the molding area 112 is defined by the dimension of the opening of the top mold chest of the top mold which can not be adjusted. The dimension of a top mold chest also limits the volume of the encapsulant 113 disposed on the substrate strip 110. Normally, a molding refuse ring in the peripheries of the molding area 112 are kept around the substrate units 111 in an array to make the dimension of a molding area 112 slightly larger than the one of the substrate units 111 inside the molding area 112. The top mold touches the edges of the molding refuse ring in the molding area 112 outside the substrate units 111 to avoid damaging to the substrate units 111 and to assure that every substrate unit 111 has the same volume of encapsulant 113.
When the dimensions or the locations of the chip 112 are different or the dimensions of the substrate units 111 are changed, the gaps from the edges of two parallel side rails of the molding refuse ring parallel to the mold flow direction to the closest chip is changed as well. When the gaps are larger, the speeds of mold flow 132 at the side rails inside a molding area 112 along the gaps are faster as shown in FIG. 1. The encapsulant 130 will be unevenly molded. Once the mold flow speeds 132 at the side rails are much faster than the mold flow speeds 131 at the center, and then molding issues will be encountered such as encapsulated bubbles or voids.